Magnetic resonance imaging (MRI) is a common and well-known technique for imaging the internal structure of objects and for medical diagnosis. MRI requires that the object to be imaged be placed in a uniform (typically to within 1-10 ppm) and strong (typically in the range of 0.5 to 1.5 Tesla) magnetic field. Generating such magnetic fields is difficult and expensive.
A concern in designing MRI devices for medical imaging is open access to the patient. Some patients are claustrophobic and are very uncomfortable in a magnet bore. Also, some medical procedures are best performed with visual access to the patient or patients face. For example, visual contact with the patient is particularly important during a cardiac stress MRI study where the heart is imaged while being stressed. Without visual contact during the stress study, the procedure would need to be interrupted every time the patient feels discomfort to assess the gravity of the complaint. Even more serious is the possibility of missing an indication of patient deterioration, which could lead to grave consequences for the patient.
Typically, MRI homogeneous magnets for full-body imaging have a magnet length of about 150 cm, with the field of view (FOV) located in the center of the magnet. For cardiac imaging, the patient must be placed in the magnet so that the patient's heart is centered in the FOV. For all but perhaps the tallest patients, the patient's face cannot be seen from outside the magnet. Also, for imaging body parts other than the lower extremities, visual access to the patient's face is cut off.
MRI equipment manufacturers have attempted to make magnets as short as possible so patients within the magnet are not so inaccessible and uncomfortable. The relation between magnet cost and magnet length is generally not well understood in the art.
It would be an advance in the art to provide short MRI magnets that provide a relatively large FOV at reduced cost. Particularly, it would be an advance to provide magnets short enough for cardiac imaging while allowing visual access to the patient's face.